It is known that Polybenzimidazole(PBI) based on diaminobenzidine (DAB) and isophthalic acid (IPA) as PBI-I and is soluble in polar aprotic solvents such as N,N-dimethyl acetamide [Li et al. Chem. Mater. 15 (2003) pp. 4896-4915]; while AB(polybenzimidazole) (ABPBI) is soluble only in strong acids such as sulfuric acid, formic acid, trifluoroacetic acid, phosphoric and poly(phosphoric acid) [Asensio et al. Fuel cells 5 No. 3 (2005) pp. 336-343]. Monomer cost and synthesis time for ABPBI are much lower than that for PBI-I.
Chung et al. in U.S. Pat. No. 4,842,740 disclosed a membrane prepared from the blend of polyarylates with PBI-I polymer. The addition of polyarylate to the polybenzimidazole membrane allows the composition to be more thermally processable and less susceptible to moisture. These membranes show high regeneration capacity while retaining good flux ranges.
Asensio et al. in J. Electrochem. Soc. 151 (2) (2004) pp. A304-A310 prepared membrane based on poly(2,5-benzimidazole) (ABPBI) by simultaneously doping and casting from ABPBI/phosphoric acid/methane sulfonic acid solution. However, these membranes are used for polymer electrolyte membrane fuel cell (PEMFC).
Wang et al. in AIChe 52 (2006) pp. 1363-1377 reported PBI based nanofiltration (NF) membranes (hollow fibers) with mean effective pore radius of 0.348 nm for cephalexin separation, which was dependent on the pore size and the electrostatic interactions between solute and the membrane.
Wang et al, J. Membr. Sci. 281 (2006) pp. 307-315 prepared PBI based NF membranes with molecular weight cut-off (MWCO) of 525 Da exhibited V-shaped chromate rejection curve with an increase in pH.
The above prior arts show PBI based porous membranes are based on (poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole) (PBI-I) polymer. However, these PBI membranes suffer from drawbacks with respect to stability and solubility in solvents such as NaOH (2.5N) and H2SO4 (25N). Dense ABPBI membranes with good thermo chemical properties are known for PEMFC applications, but are not known for their stability towards strong acid, bases and organic solvents.
Therefore there is a clear need in prior art for porous ABPBI membranes with stability to acids, bases and solvents. Further the need for porous ABPBI membranes that can withstand concentrated acid, base and organic solvents under harsh operating conditions has not been addressed by prior art documents.